The present invention relates to a method of regulating an internal combustion engine, in particular with a lean operating mode, in order to reach presettable nitrogen oxide emission values of the internal combustion engine. The invention also relates to a corresponding regulator and internal combustion engine.
It is already known from EP 0 259 382 B1 to operate an internal combustion engine for driving an electric generator with constant nitrogen oxide emission values, by regulating the mixture pressure before the inlet valves of the cylinders according to the electric output delivered by the generator. The target value of the mixture pressure in the intake before the inlet valves is taken from a characteristics field which shows the dependency of the mixture pressure on the delivered electric output with constant emission values. The measured actual value of the pressure before the inlet valves is then regulated, via an adjustment of the fuel-to-air ratio in a gas mixer, to its target value determined via the characteristics field. The characteristics field used for this is produced by gauging at least two operating points with identical NOx emission values. It is possible, through this previously known method, that an internal combustion engine can very precisely observe the desired emission values in a wide output range. The system known from the named European patent has the advantage that there is practically no wear and ageing of sensitive sensors.
A further improved system according to the preamble is presented in the European patent application EP 1 225 330 A2, in which the regulation scheme known from EP 0 259 382 B1 has been supplemented by an ignition point adjustment in order to provide, in every operating condition, a regulation reserve for rapid reaction to load changes. This regulation also serves to always run the internal combustion engine with an optimum degree of efficiency.
Each of the previous regulation methods is designed only for operation with one fuel type. However, there are also internal combustion engines—principally stationary—which are operated with two different fuel types. No regulation method with which the reaching of presettable nitrogen oxide emission values is assured is known to date for such engines.